Understanding Hearing Above Water

To grasp the mechanics of hearing in air, imagine I'm on a hilltop, yelling as if I were giving birth to a porcupine.

When I scream, I push air from my lungs through my vocal cords, causing them to vibrate. This vibration sets nearby air particles in motion, creating a chain reaction of vibrating particles. The air is dense enough that these vibrations travel through it, forming sound waves that eventually reach your ears.

When sound waves travel, they don't go in a straight line. Instead, they disperse in a spherical pattern from the source. The structure of your ear helps channel these sound waves into your ear canal, where they vibrate against your eardrum, triggering the ossicles—three tiny bones that amplify the sound to the cochlea. The cochlea, filled with fluid, converts these vibrations into signals that your brain interprets as sound.

How We Identify Sound Direction

To recognize the origin of a sound, our brains rely on two main cues: interaural time difference and interaural level difference.

1. Interaural Time Difference: When a sound wave approaches, it doesn't reach both ears simultaneously. For instance, a sound from your left ear will hit your left ear before the right. This time difference helps your brain localize the sound's source.
2. Interaural Level Difference: The volume of sound reaching each ear also assists in determining direction. If a sound is louder in one ear, it likely comes from that side.

However, underwater, sound waves travel approximately 4.3 times faster than they do in air. This rapid travel means your brain struggles to detect the time gap between sounds reaching your ears, making localization more challenging.

The first video titled "How Do We Hear Underwater?" discusses the intricacies of sound perception in aquatic environments. It delves into why our usual auditory cues become unreliable when submerged.

Interaural Level Differences Underwater

Volume differences between ears can also guide sound localization. In air, if a sound is louder in one ear, it's easier to determine its direction. However, underwater, sound doesn't attenuate as much. You may have noticed this when hearing pebbles clinking underwater, where sounds can be surprisingly clear.

Why Sounds Seem to Emanate from Within

Have you ever wondered why you can't hear a fish yelling in its bowl? If it could, you'd only hear it if your head were submerged. Sounds traveling from underwater to above hit a boundary that reflects most acoustic energy back into the water, making it difficult to hear.

Inside your ears, a similar phenomenon occurs. When submerged, air remains trapped in your ear canal, creating a water-air boundary. Sound waves hitting this boundary reflect rather than penetrate, preventing your eardrums from vibrating.

Despite this, sound can still reach your cochlea through bone conduction, allowing you to perceive underwater sounds, albeit in a muffled manner. This unique conduction process explains why sounds seem to originate from inside your head.

Wrapping Up: The Challenges of Underwater Sound Localization

The difficulty in pinpointing the source of underwater sounds stems from our auditory system's evolution, which is not adapted to an aquatic environment. Water's density alters how sound waves travel, hindering our ability to process timing and volume differences between ears effectively.

Yet, with experience, some individuals can learn to locate underwater sounds more accurately. Notably, "fish listeners" in Malaysia have honed their skills to identify fish by listening to the sounds they produce.

The second video titled "How Good Can You Hear Sounds Underwater?" explores the limits of human sound perception in water and highlights techniques for improving underwater hearing.